Eight sixth-grade students received individualized instruction on the addition and subtraction of fractions in a one-to-one setting for 6 weeks. Instruction was specifically designed to build upon the student's prior knowledge of fraction ideas and to emphasize estimation. It was determined that all students possessed a rich store of prior knowledge about estimation that was focused on parts of wholes in real world situations. On their own initiative, students related fraction symbols and procedures to prior knowledge about estimation in ways that were meaningful to them and accurately estimated sums and differences prior to learning computational algorithms. (PK)